EBOD common mistakes
EBOD · Understand the traps and how to avoid them.
When a question gives a refraction at one plane (e.g. corneal plane for a contact lens) and asks for the prescription at another, the candidate applies the vertex-distance formula in the wrong direction, or changes the cylinder axis by 90° but forgets to invert the sign of the cylinder power when converting between plus- and minus-cylinder form.
The formula is memorised as a string of symbols rather than as a physical relationship, and sign conventions are not written down during the calculation, so a single slip goes unnoticed.
What to do instead
Before calculating, draw a simple diagram with the correcting lens, the vertex distance and the eye, label which plane the given power refers to, and state the conversion (F_new = F/(1 - dF)) with the sign of d fixed; for cross-cylinder conversions, always write the three steps (sum, sign change, axis rotation) explicitly and check by reconverting back to the original form.
For a contact-lens wearer with a corneal infiltrate or ring-shaped lesion, the candidate answers with a single topical antibiotic (or antibiotic plus steroid) and never mentions that the lens and case should be sent for culture, that Acanthamoeba and fungal keratitis must be considered, or that the epithelium over the lesion should be scraped for microscopy.
Pattern-matching to 'contact lens + red eye = bacterial ulcer' shortcuts the exposure history and the morphology of the infiltrate, which are what actually discriminate the organisms.
What to do instead
Adopt a fixed template for every microbial keratitis answer: (1) risk/exposure history including lens type, water contact and case hygiene, (2) scrapings for Gram/Giemsa/calcofluor and culture before treatment, (3) organism-specific empirical therapy, (4) explicitly name the two alternative diagnoses you are excluding and the finding that would change management.
In an intraoperative complication scenario the candidate writes 'convert to extracapsular extraction' and stops, omitting anterior vitrectomy, a search for retained nuclear fragments, and a plan for IOL placement (anterior chamber, sulcus, or aphakia) with the corresponding wound management.
The answer is recalled as a single keyword from a list of complications rather than as a stepwise intraoperative decision tree.
What to do instead
Rehearse the posterior capsule rupture answer as a numbered sequence in a fixed order: recognise and stop phaco, viscoelastic, anterior vitrectomy with a cutter, inspect for nuclear material and remove it, decide on IOL type and position, then state the postoperative plan and the counselling point about retinal detachment risk.
For a painful red eye with a hazy cornea and a mid-dilated fixed pupil, the candidate lists pilocarpine as the first-line agent, or uses pilocarpine before lowering the pressure, and omits systemic aqueous suppression and corneal indentation.
Old teaching that miotics 'open the angle' is retained without the caveat that a swollen, ischaemic iris will not respond until the pressure is brought down.
What to do instead
Write the acute angle-closure order set in a fixed sequence - topical beta-blocker/alpha-agonist/apraclonidine-type agents plus topical steroid, systemic carbonic anhydrase inhibitor, osmotic agent if needed, corneal indentation, then pilocarpine once the pressure is falling, followed by definitive laser peripheral iridotomy to both eyes - and state the timing of each step.
Sudden painless monocular loss of vision in an older patient is attributed to cataract, vitreous haemorrhage or 'ischemic optic neuropathy' without first explicitly testing and documenting for a relative afferent pupillary defect and considering retinal artery occlusion with its systemic urgency.
The differential is generated from the patient's age and comorbidity rather than from the examination findings, and the afferent pathway is not tested as a reflex first step.
What to do instead
For every 'sudden painless vision loss' stem, run the same four-branch check out loud in the answer - vascular (artery/vein occlusion), vitreous haemorrhage, retinal detachment, optic nerve - and state the pupillary finding, fundus finding and the immediate systemic work-up (ESR/CRP, carotid and cardiac assessment) before committing to a diagnosis.
A chronic, unilateral, low-grade anterior uveitis in a child or young adult is labelled idiopathic and treated with topical steroid alone, with no mention of juvenile idiopathic arthritis screening, chronicity markers (band keratopathy, posterior synechiae), or the need for systemic immunosuppression if it is steroid-dependent.
The adult idiopathic anterior uveitis template is applied to a paediatric case, and the absence of symptoms is read as absence of disease.
What to do instead
Attach a mandatory 'system enquiry' to every uveitis answer - age, laterality, chronicity, systemic symptoms, targeted serology/imaging, and a named masquerade or systemic association for that specific demographic - and state explicitly what would trigger referral for systemic therapy.
A visual field defect that respects the vertical midline is described as glaucomatous, or a bitemporal defect is mislabelled binasal, without stating the chiasmal/supra-chiasmal localisation or which investigations follow.
Fields are read as pictures rather than by first establishing whether the defect is monocular or binocular and whether it respects the vertical or the horizontal meridian.
What to do instead
Force a two-question routine before naming any field defect: is it present in one eye or both (bow-tie/chiasmal vs retinal/optic nerve), and does the border respect the vertical midline (retrochiasmal)? Then state the localisation and the next test (pituitary protocol MRI, neuroimaging, or ocular work-up) in the same sentence.
A child with an esotropia and hypermetropia is scheduled for strabismus surgery in the answer, without first prescribing the full cycloplegic refraction, assessing amblyopia and stereoacuity, or mentioning that a fully accommodative esotropia is managed with glasses (plus/minus bifocals) rather than surgery.
The adult strabismus reflex (operate on the angle) is applied to a paediatric case, and the accommodative component is not separated from the constant or intermittent deviation.
What to do instead
For every childhood esotropia, structure the answer as: cycloplegic refraction and full correction first, re-assess the deviation with glasses and at near with a bifocal if needed, treat amblyopia (occlusion or atropine) concurrently, then state the specific findings (residual angle, AC/A, high AC/A ratio, incomitance) that would justify surgery.
A watering, irritated eye is diagnosed as dry eye and treated with lubricants without any test of lacrimal outflow - no fluorescein dye disappearance test, no sac syringing, no assessment for punctal or canalicular stenosis, and no distinction between hypersecretion and obstruction.
'Watering' is filed under 'dry eye' because both present with tearing and irritation, and the outflow system is never examined in a routine slit-lamp answer.
What to do instead
Make a three-step outflow check routine in any epiphora answer: dye disappearance test (retention implies outflow obstruction), sac syringing with the patency and reflux findings stated, and examination of the punctum, lid position and lacrimal sac; then commit to a level of obstruction (punctal, canalicular, sac, nasolacrimal duct) with the matching procedure.
For a young child with a white pupillary reflex and an intraocular mass, the candidate proposes fine-needle aspiration, vitreous sampling or biopsy to establish the diagnosis.
The general oncology rule 'tissue diagnosis before treatment' is applied without the ocular oncology exception, and retinoblastoma is not considered in the differential for a leukocoria stem.
What to do instead
Memorise the hard rule that an intraocular mass in a child is retinoblastoma until excluded and is never biopsied because of the risk of extraocular seeding; the answer must state imaging (ultrasound, MRI of orbits and brain), examination under anaesthesia by an ocular oncologist, staging for germline disease, and referral to a specialist centre before any intervention.
The candidate answers a question that was not asked - producing a long differential list when the stem asks for the single most likely diagnosis, or giving a diagnosis when it asks for the immediate next step - and leaves units, laterality or the time frame unspecified in the answer.
Under time pressure the response is written as a stream of recalled facts rather than being checked against the exact wording of the stem, and exam technique is rarely rehearsed compared with content.
What to do instead
Underline the operative words in every stem (most likely, next step, most appropriate investigation, initial management) before writing, keep an answer to the number of lines the marks allow, and finish every clinical answer with an explicit statement of laterality, timing and units; in practice, do timed full papers and mark strictly against the wording.